Solution-processed Synthesis And Fabrication Of Cu₂ZnSnS₄（CZTS） Nano Materials And Thin Films And Their Photovoltaic Property

Copper indium gallium selenide (CIGS) solar cell has made significant progess as an importantthin film solar cell. Earth abundant kesterite opper zinc tin sulfide (CZTS) semiconductor has lots ofsimilarities to CIGS in its crystal structure and optoelectronic properties. CZTS semiconductorshave an optical band gap of1.5eV, which is closer to the optimal optical band gap in theory forphotovoltaic devices. Moreover, its compositional element has less toxicity than CIGSsemiconductors. As a result, CZTS will be a very promising alternative to CIGS. If success, therequirements of rare and expensive indium in developing high efficiency can be avoided, toxicitycan be reduced, and low cost and more environmental-friendly solar cells can be expected.Aiming at the current fabrication situation of CZTS solar cells, this thesis focuses onsolution-processed fabrication of CZTS solar cells, which can be be divided into the following twoparts.Firstly, we synthesized CZTS particles using solvothermal method and hot injection methodrespectively. Then, the two samples were characterized in crystal structure, morphology and particlesize. The results showed that the particles synthesized using the solvothermal method always have amicrometer scale size and the morphology is not easy to control, which will be an adverse factor inthe fabrication of CZTS thin films; while by hot injection methods nanometer scale and relativeuniform morphology of CZTS particles can be obtained with high quality. Moreover, focusing onthe nontoxic synthesis of CZTS nanoparticles using hot injection methods, a safe and nontoxicsolvent polyethylene glycol (PEG) was firstly used to substitute oleylamine which was used inmany literatures.Secondly, based on the above nanoparticles by hot injection with nontoxic solvent,“ink” ofCZTS nanoparticle was prepared by dispersing the PEG based nanoparticles into relative solvent.Then, CZTS thin films were prepared by two methods of spin coating and electrospray methods.The experiment showed that the electrosparyed film was more uniform and dense and the filmthickness can be easily controlled compared to spin coated ones. In order to further verify the photoactive properties of the material, the photoconductive test was performed on the electrosprayedCZTS thin films and a simple hybrid heterojunction device was designed and fabricated. Thecurrent-voltage curves revealed that the conductivity of the CZTS films has a significantly increase under illumination and the synthesized PEG based CZTS nanoparticles as well as the electrosparyedfilms can be successfully applied to photovoltaic devices.